Hi,
Just came back from mongolia, at one time in -15 degrees in the morning... You my wanna read up more in the tread web sent by others...As for me just my 2 cent
1) Yes, bring extra batteries, keep the battery warm in your jacket. And i usually keep it in a small sack that i sleep with in my sleeping bag.. ..areas with no electricity, i'll bring more batts, but otherwise if going for long period, would consider a solar battery charger. I would bring my film SLR bodies as a back up!
2)Place the camera in a waterproof sack or ziplock bag when moving from warm house/tent to a cold outdoor and vice versa....as condensation would/may inflict damage to the electronics. Do dust off the snow before it melt indoors...with a fine brush, i use a $1.00 1/2 inch brush.
3)Try and avoid changing lens in outdoor....I Learnt it a hard way! if you really need to do it...do it indoor, or do it in a clean bag... switch off camera, point body facing down and swap the lens carefully....don't rush. lens drop, break,
Do practise it untill become natural for you. Otherwise. consider carrying a 2nd body. As for me. i forcast my theme for the day....landscape day ,use my 18-55mm kit, portrait day/night use my 50mm, long lens day,,,my 70-300mm etc.... I improvise alot using what lens i had attached on.
4)conserve power....i reduce the need to review the pictures too much. LCD screen uses more power.
Anyway... just read more and enjoy shooting! please bring a back up. be it point and shoot (PNS) or film camera (rarely need batteries!)